Coating finishes, particularly exterior coating finishes in the automotive industry, are generally applied in two or more distinct layers. One or more layers of primer coating composition may be applied to the unpainted substrate first, followed by one or more topcoat layers. Basecoat-clearcoat composite coatings are particularly useful as topcoats for which exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired. The basecoat layer contains the colorants that provide the color for the topcoat, while the clearcoat layer provides a smooth, glossy finish. The automotive industry has made extensive use of these coatings for automotive body panels.
The colorants in automotive basecoat compositions are typically one or more dispersed pigments. Pigment dispersion in the composition must accomplish at least two objectives. First, the pigment should be as fully wet-out as possible for optimum color development in the coating layer. Secondly, the pigment should be stabilized against hard settling and re-agglomeration of the pigment particles so that the basecoat composition will have a reasonably long shelf-life. Many types of dispersants have been suggested for solventborne compositions. The options for waterborne compositions has been more limited, as the dispersant must itself be water-dispersible. Nonetheless, waterborne basecoat compositions are in need of the same good color development and stability as solventborne basecoat compositions. A pigment dispersant useful in both solventborne and waterborne compositions would simplify manufacturing and storage because the same dispersant intermediate could be synthesized and used to made pigment dispersions for either solventborne or waterborne compositions.